Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
per-tĕro, no perf., trītum, 3, v. a., to rub, bruise, or pound to pieces: myrti bacam, Col. 12, 38, 7: uva pertrita, id. 8, 5, 21.
1. pertrītus, a, um, Part., rubbed to pieces; from pertero.
2. per-trītus, a, um, adj., quite worn out, very hackneyed or common, very trite (post-Aug.): quaestio, Sen. Contr. 7, 18, 7: scio pertritum jam hoc esse, Sen. Ep. 63, 10.